def is_prime(n):
    if n < 2:
        return False
    else:
     for i in range(2, n):
        if n % i == 0:
            return False
    return True

if is_prime(4) == False:
    print("不是素数")
else:
    print("是素数")

#递归实现阶乘
def factorial(n):
    if n == 1:
        return 1
    else:
        return n * factorial(n-1)

print(factorial(5))





